Boiler drop plug



y 2 1941- R. N. MILLER 2,242,798

BOILER DROP PLUG Filed June 6, 1940 INVNTOR: Eaberi M BY W W A TTORNEYS.

Patented May 20, 1941 BOILER DROP PLUG Robert N. Miller, Rosemont, 'Pa.,assignor to The Pennsylvania Railroad Company, Philadelphia, Pa., acorporation of Pennsylvania Application June 6, 1940, Serial No. 339,079

1 Claim.

This invention relates to safety plugs for steam boilers and, moreparticularly, to the type comprising a tubular body-member with adrop-plug normally sustained therein by a fusible bushing adapted, undera given temperature, to melt and release the drop-plug, whereby escapingsteam will eiiect an audible Warning that the water in the boiler haslowered to an undesirable level.

The primary object of this invention is to provide an improved drop-plugof the indicated species including novel features whereby the emciencyis greatly enhanced.

Another object is provision of a drop-plug of the type above referred tothat is devoid of any creeping or sticking tendencies, which is simpleto manufacture, easy to install, cheap in production, and withal ispositive and reliable in action.

Other objects and ancillary advantages of this invention will appear asthe nature thereof is better understood, said invention consistingsubstantially in the novel features of construction, combinations andarrangements of parts herein fully described and illustrated by theaccompanying drawing; wherein similar reference characters are used todesignate corresponding parts throughout the several views; and thenfinally pointed out and specifically defined in the concluding claim.

In the drawing:

Fig. 1 is a vertical section through one typical form of drop-plugconstructed in accordance with this invention, and preferably adaptedfor application in locomotive boiler crown sheets, a fragmentary portionwhereof is shown.

Fig. 2 is an underside plan view of the same.

Fig. 3 is a perspective View of a fusible-bushing included in thedrop-plug structure.

Fig. 4 is a perspective view of the releasable component or drop-plugdetached from the associated body-member.

Fig. 5 is a section similar to Fig. 1 of a slightly modified form of theinvention.

Fig. 6 is an underside plan view of the preceding figure.

Fig. 7 is a central vertical section through a further typical form ofthe invention; and,

Fig. 8 is an underside plan view of the said figure.

In the following detailed disclosure of the embodiments of thisinvention shown by the accompanying sheet of drawings, specific termswill be employed for the sake of clarity, but it is to be understoodthat such terms are used in a descriptive sense and not for purposes oflimitation.

Each specific term is intended to include all technical equivalentswhich serve in a similar manner to accomplish an analogous purpose.

In the practice of this invention, and referring descriptively to theembodiment thereof, shown more particularly by Figs. 1-4, inclusive, thebody-member of the drop-plug is comprehensively designated by thenumeral I, said member consisting preferably of a machined annular bodyportion including a taper-bored upper part 2 and an externallytaper-threaded lower part 3, for screw engagement in acorrespondingly-threaded aperture 5, provided for its reception in thecrown-sheet 6.

Interiorly, the body-shell portion 3 is appropriately formed to define apolygonal-shaped socket l for insertion of a suitable key whereby thesaid member is threaded into or drawn-out of the crown-sheet aperture 5;and said socket has an adjoining annular groove 8, for preventingformation of burr during finishing of the socket, with a relativelysmaller 'counterbore 9 communicating with the lower end of the plug mainbore II]. This bore 10, it is to be particularly noted, is preferablyoutwardly divergent in form, substantially approximating to athreequarter inch taper in a longitudinal dimension of one-foot; and itis conveniently press-fitted with a scomplementally-taperedfusible-bushing ll. Into this bushing l I is press fitted the releasableclosure or drop-plug 12, said plug having a taper conforming with thatof the bore Ill, the major or upper end l3 having a diameter slightlyless than the smaller diameter of said bore. Creeping of the plug l2 inservice is thus eliminated by compression of the fusible-bushing ll,incidental to the press-fit application of said plug; while sticking iseiiectively prevented when the plug I2 is released for blowing out. Inaddition, the drop-plug I2 may be provided in its smaller end M with anaxial recess l5 for purposes of proper centerin of said plug, relativeto the bore Ill, when such plug is initially secured in position eitherby a pressure operation, or otherwise.

Incidentally, it is here remarked that the externally screw-threadedportion 3 is of a taper substantially approximating that of the bore l0and plug I2, but reversely inclined to positively ensure an absolutelyliquid-proof joint within the crown-sheet 6. The fusible-bushing ll maybe produced by casting, extrusion, or expanding of a suitable alloytubing, cut to the desired lengths, and prefer-ably composed of fifteenper cent tin with eighty-five per cent lead; while there is no sweatsolder bond between the shell I served that the screwthreaded portion 3,of the cast shell 9, is formed with a plain annular extension H! of lessdiameter, said extension having diametrically opposed notches IQ forapplication thereto of a conventional spanner-wrench, or othermanipulator, whereby the shell I can be In addition thereto, thedrop-plug l2 shell I, so as to provide an extension 2! in the fireboxarea to serve as a means for accelerating heat conduction to thefusible-bushing II. In

this form of the invention, an annulus 22 .of the bushing fusiblecomposition may be extruded or otherwise applied around the plugextension 2|, as indicated in broken line section, at the base of thebore l0.

1 easily engaged in or removed from the crownsheet 6. is lengthened toproject well below the tapering bore l0, into the cylindrical hollowZDof the From the foregoing it will be readily apparent that inthe eventof low water in the boiler, or over the crown sheet 6, which results inuncovering the top portion [3 of the drop-plug I2, the fusible bushing II, that normally is mechanically held to the shell I and said plug,becomes overheated sufficiently to melt and releases the dropplug l2,whereupon the latter is blown out by steam pressure in the boiler intothe firebox, it being, obvious that the tapering formation of said plugefiectively prevents creeping or sticking; as well as greatlyfacilitating its release when the fusible-bushing commences to melt.

Having thus described my invention, I claim:

A drop plug for attachment in the crown sheets of boiler furnacescomprising an annular component having a uniformly and downwardlytapered bore, a conformatory bushing of fusible material and eventhickness fitted in said bore, and a frusto-conical plug of complementaltaper engaged in the bore of the fusible bushing, said plug having itslarger end of slightly less area than that of the smaller end of theaforesaid annular component bore.

ROBERT N. MILLER.

